Five Heatwaves Leave SE Europe's Grid Operators Short of Evening Flexibility
Five heatwaves across four countries exposed how thin dispatchable backup capacity remains in south-eastern Europe once solar output drops after sunset.
Montel published a grid flexibility assessment for south-eastern Europe on Friday (2026-08-28), finding that five heatwaves across four countries this summer stretched power systems to the point where a shortage of fast-response backup capacity left grid operators unable to adequately cover evening cooling demand.8
The solar performance masked the underlying problem. Europe's solar panels produced 17 percent more electricity during the heatwave periods than their seasonal average, according to Ember data reported by Canary Media on Tuesday (2026-08-25), with clear skies and peak irradiance aligning neatly with peak afternoon cooling demand. After sunset, both generation and the relief it provided disappeared. Temperatures across south-eastern Europe stayed elevated well into the night, sustaining air-conditioning loads that grids without adequate fast-response capacity struggled to serve.5
Battery storage helped elsewhere. Europe added 36 gigawatt-hours of new battery capacity in 2025, up 48 percent year-on-year according to Canary Media. In south-eastern Europe, where storage deployment has lagged wealthier western markets, the evening shortfall showed.5
Drought deepened the squeeze. Low river levels cut output from run-of-river hydro plants across the Balkans and reduced the reservoir headroom that operators rely on as a fast-dispatch buffer. ENTSO-E's Summer Outlook, published on Wednesday (2026-06-03), had already flagged limited interconnection capacity in peripheral markets and natural gas supply constraints in Moldova as risks requiring close monitoring if summer conditions proved severe. They did.2
Nuclear offered little additional buffer. European nuclear plants faced rising river temperatures during peak heat periods, cutting cooling water availability and forcing output reductions at some units at the worst possible moment, Oilprice.com reported on Wednesday (2026-08-26).7
The UK's eclipse on Wednesday (2026-08-12) offered a separate illustration of what adequate — if expensive — grid balancing looks like under acute stress. NESO paid up to EUR 750 per megawatt-hour to stabilize the system, analysts told Montel on Thursday (2026-08-13). The UK passed. South-eastern Europe faced not a single discrete event but a sustained multi-week test, with fewer fast-dispatch tools available when the heat held.4
Walburga Hemetsberger, chief executive of SolarPower Europe, told Canary Media that evening cooling persistence is now a design constraint grid planners must build around. "Temperatures often remain high after sunset and AC demand can stay elevated, even as solar production declines," she said.5
France has moved toward a capital response. State-owned EDF plans to spend more than $10 billion over 15 years adapting its nuclear and hydropower fleet to higher temperatures and lower water availability, including new infrastructure to cool discharge water from nuclear plants — a cost category absent from utility planning assumptions a decade ago.5
Data center load growth adds another variable. ENTSO-E warned in May (2026-05-08) that grid operators across Europe may be forced to curtail renewable energy penetration if data center expansion is not properly managed, a direct constraint on decarbonization pathways.1 Google's plan for a 1-gigawatt data center in Belgium with flexibility commitments, reported by Energy Voice on Tuesday (2026-08-04), is one model for binding large industrial loads to grid obligations. Replicating it across south-eastern Europe's less liquid power markets would require regulatory frameworks and grid depth that do not yet exist.3
Montel market expert Noemie Baud concluded in a Wednesday (2026-08-26) analysis that flexibility was the variable separating countries that managed summer stress from those that did not. Moldova, whose dependence on constrained gas supply was identified by ENTSO-E before the summer as a specific vulnerability, enters the autumn with no announced backstop capacity in place.6,2